1. Field of the Invention
The present invention relates to a hybrid type compressor which is driven by different driving sources such as an engine and an electric motor.
2. Description of Related Art
JP-U-6-87678 discloses a hybrid type compressor for vehicle air conditioning apparatus, in which the compression mechanism thereof is driven by an electric motor when an engine stops, and is driven by the engine when the engine operates.
In the hybrid type compressor disclosed in the above reference, because a swash plate constructing the compression mechanism is connected to the motor shaft of the electric motor, the rotor of the electric motor rotates even when the compression mechanism is driven by the engine.
As a result, the inertia moment of a rotating system including the swash plate and the rotor becomes large, and an impact vibration caused by engaging an electromagnetic clutch therewith becomes large, thereby making a passenger feel uncomfortably.
JP-A-4-164169 discloses a hybrid type compressor in which the rotational driving force of an engine is transmitted to the compression mechanism thereof through an electromagnetic clutch. In this hybrid type compressor, a discharged refrigerant amount is adjusted by ON-OFF controlling the electromagnetic clutch when the compression mechanism is driven by the engine, while it is adjusted by controlling a current amount supplied to an electric motor when the compression mechanism is driven by the electric motor.
Recently, the electromagnetic clutch is replaced by a variable capacity mechanism to change the discharged refrigerant amount for eliminating the impact caused by engaging the electromagnetic clutch therewith.
However, adding the variable capacity mechanism to the hybrid type compressor results in that the total cost of manufacturing the same increases.
Further, the performance of a refrigeration cycle mainly depends on the product of the volume of the compression chamber in the compression mechanism and the rotational speed thereof. Therefore, the volume of the compression chamber needs to be set in accordance with the demanded performance of the refrigeration cycle and the rotational speed of the driving source to drive the compression mechanism.
Accordingly, in the compression mechanism to attain the demanded refrigeration cycle performance when the volume of the compression chamber is enlarged and the rotational speed of the compression mechanism is lowed, a driving torque to drive the compression mechanism becomes large, thereby making the size of the electric motor unit large.
As described above, when the compression mechanism is driven by different driving sources, it is difficult to harmonize the characteristics of the driving sources and the compression mechanism with each other.